1. Technical Field
Embodiments of the invention relate generally to power converters. Other embodiments relate to non-isolated full bridge power converters.
2. Discussion of Art
Power supplies are electronic/electrical circuits that supply electric power to one or more electric loads. The term “power supply” is most commonly applied to collections or an assembly of electrical devices that convert one form of electrical energy to another, which are commonly referred to as “power converters.” Many power supplies include two or more power converters connected together. Typically, power converters are “switching” power converters, in which multiple solid state devices are used to intermittently interrupt an input current so as to effectuate conversion of the input current to an output current having different amplitude, voltage, and/or frequency. For example, a “DC power converter” produces output power at a substantially constant output voltage and/or current.
Conventional power converters, generally, are groupings of plural solid state switches that are connected to output terminals from a first DC input terminal or from a second DC input terminal. Paired DC terminals typically are known jointly as a “DC link,” while the term “DC link voltage” often is used to refer to an electrical potential difference across this DC link. Thus, a conventional DC-DC power converter is connected between an input (primary) DC link and an output (secondary) DC link.
Power converters can be “isolated” or “non-isolated.” In an isolated power converter, a transformer electromagnetically couples a primary circuit of the power converter to a secondary circuit of the power converter. In other words, there is no direct electrical connection between the primary DC link and the secondary DC link. By contrast, a non-isolated power converter electrically connects the primary DC link with the secondary DC link.
Power converters can be “half bridge” or “full bridge.” A half bridge power converter switches current in only one direction to a load, that is, polarity is maintained across the primary and secondary links. In contrast, a full bridge power converter can switch current in either direction to the load, fully commuting the current so that polarity can be inverted from the primary link to the secondary link.
The instant invention relates principally to non-isolated full bridge power converters. One example of a non-isolated full bridge power converter is a “dual buck” power converter.
In a typical buck power converter, a first switch, a first inductor, and a first diode form a three-way node between the first DC input terminal, a first output terminal, and the second DC input terminal. In operation, the first switch is intermittently cycled, and the first inductor smoothes resultant voltage surges to produce an averaged high voltage at the first output terminal that is less than the voltage at the first DC input terminal. In a “dual buck” power converter, a second switch, a second inductor, and a second diode form a second three-way node between the second DC input terminal, a second output terminal, and the first DC input terminal. The second switch also is intermittently cycled, in some embodiments synchronously, with the first switch, to produce an averaged low voltage at the second output terminal. The first switch, first inductor, and first diode may be referred to as a first “leg” of the converter that connects the first and second input terminals with the first output terminal; while the second switch, second inductor, and second diode form a second leg of the converter that connects the first and second input terminals with the second output terminal.
The symmetry of the dual buck power converter makes it attractive for operating in DC systems isolated from ground, because in an ideal operation the first and second branches are under the same V and I stresses. However, the circuit has an undesirable behavior under common mode perturbations. Those perturbations can be originated, for example, by jitter (asynchronicity or time difference) in the switching of active power semiconductors (exemplary solid state switches). The effect of jitter in the dual buck topology is to create large spikes in the output terminal voltages with respect to ground at the input and output DC connections. Such spikes stress the electrical insulation of the circuit components and can severely affect the converter lifetime.
In view of the above, it is desirable to provide a dual buck converter topology in which common mode perturbations are mitigated.